Process for flameproofing paper



; but also of the combustible rosin size.

United States Patent 1 7 2,867,549 PROCESS FOR FLAMEPROOFING PAPER Charles R. Outterson, Richmond, Va., assignor to The Albemarle Paper Manufacturing Company, Richmond, Va., a corporation of Virginia No Drawing. Application March 6, 1956 Serial No. 569,689 13 Claims. (Cl. 117-137) fiameproofing properties and the desired water resistance normally imparted by the size.

The object of this invention is to provide a process for fiameproofing paper with water-soluble fiameproofing salts wherein a substantial degree of water resistance is imparted to the fiameproofing agents.

Still another object is to provide a process for makin'g' rosin sized paper containing water-soluble fiameproofing salts, which is characterized both by a high degree of flameproofness and excellent size properties, including good water resistance.-

Broadly speaking my invention comprises impregnating an at least partially sized paper with an aqueous solution of the fiameproofing salts containing finely divided rosin in stable dispersion, the fiameproofing salts being characterized by a maximum pH of about 7 and preferably less, and then drying the paper in the usual fashion.

I have found that when a rosin suspension containing water-soluble fiameproofing salts dissolved in the aqueous phase is applied to a highly absorbent, namely unsized paper, a substantial degree of fire resistance is conferred on the paper but it is subject to afterglow and, therefore, 1 continues to smolder.

It cannot, therefore, meet fireproofing specifications. Thisinadequacy in the flameproofing is apparently due to the fact that the flameproofing salts, which are in solution in the aqueous phase of the suspension are rapidly absorbed into the fibers and, in effect, removed from the rosin. The rosin, which does not penetrate into the fibers, deposits on the surface of and in the interstices between the paper fibers. Because of the low concentration of protective fiameproofing salts in the deposited rosin, the rosin continues to burn, thereby giving the highly undesirable afterglow. A substantially similar situation occurs when the fiameproofing salts are introduced into the paper furnish in the beater.

However, I have found that when the paper is at least partially sized before application of the rosin despersion containing the fiameproofing sales in solution so that the rate of absorption by the fibers is appreciably reduced, a sufficient proportion of the salts remains admixed with the rosin and inhibits burning not only of the paper fibers The optimum degree ofpreliminary sizing will vary to some extent with the particular paper furnish, the weight of the finished paper and the quantity of fireproofing salts incorporated. In general, I have found that the degree of sizing shouldfbe' at least about 7 to 8 seconds in terms of water resistance as tested according to ASTM designation D 779-54. This degree of sizing gives good results, for example, with paper having a basis weight of 25 lbs.

-.per. ream ofSQO sheets, size 24.by 36 inches. For heavier ice 2 papers, it is generally desirable to have a higher degree of preliminary sizing, as, for example, about 20 to 25 seconds water resistance for a 40 lb. paper. The optimum degree of preliminary sizing for particular conditions can readily be determined by routine testing.

The preliminary sizing of the paper can be accomplished in routine fashion as, for example, in the beater with the usual sizing agents such as rosin and alum, wax size and the like.

Application of water-soluble fiameproofing salts to sized paper will satisfactorily flam'eproof the paper. However, the size properties of the paper, as for example, in terms of water resistance, are substantially destroyed. Water resistance generally drops to about 0 to'l second because the water-soluble salts dissolve and promote passage of the water through the paper. The highly soluble salts, furthermore, are completely unprotected and leach not only upon minimal contact with water but also under conditions of relatively elevated humidity.

I have found that, by applying the Waterproofing salts in the aqueous phase of a rosin suspension, the rosin, upon deposition, acts not only to size the paper, but also substantially to waterproof the water-soluble salts so that they resist leaching not only under highly humid conditions but even upon contact with water, if such contact is not unduly prolonged. For example, the treated paper, when subjected to the standard sizing test to determine water resistance retains its fiameproof characteristics after contact with the water for as long as 25 to 30 seconds or more whereas a similar paper, treated in the same way, with the exception that rosin is omitted fromsthe solution of fiameproofing salts, loses its fiameproofness within 1 second after such water contact. Prolonged immersion in Water will, of course, result in sufficient leaching of the water-soluble salts to damage fiameproofness. However, the water resistance of the salts is generally entirely adequate for most purposes and conditions of use of the paper. It will-resist, for example, prolonged periods of high humidity, dampening caused by rain or Water leakage or condensation, superficial moistening and the like.

The fiameproofing salts are preferably dissolved in any aqueous dispersion of free rosin. However, a solution of ammonium resinate can also be employed, in which case the introduction of a large amount of fiameproofing salts which are acidic in character, such asammonium sulfate or monoammonium orthophosphate, will cause decomposition of the ammonium resinate into free rosin, so that the resulting composition is in effect a dispersion of free rosin in an aqueous phase containing the flameproofing salts in solution. The use of reagents or coinponents, such as sodium r'esinate and alum, whichintroduce substantial amounts of metallic elements tendin to promote after-glow should be avoided.

. Because of the high concentrations of the flameproof ing salts in the aqueous phase, the rosin suspension should be stable to electrolytes. Such electrolyte-stable dispersions are known to the art and can be prepared in any desired manner as, for example, with the aid of a protective colloid such as gum arabic, gum acacia, casein,

animal glue, starch and the like, which stabilize the 'dis- 1 g. of a dispersing agent, such as sodium ,lignosulorthophosphate, ammonium chloride, and the like.

neutral to acid character to the mixture.

fonate, and 3 g. of a protective colloid, such as gum arabic, are dissolved in 100 cc. water and the solution heated to about 180 F. 100 g. melted free rosin are slowly poured intothe hot solution with vigorous stir-ring. To reduce the particle size of the emulsified rosin, preferably to about an average of 1 to '2 microns, the emulsion is passed through a colloid mill or other high speed dispersion apparatus.

Still another method of preparing a suitable electrolyte-stable rosin dispersion involves the liberation of free rosin particles from an ammonium resinate solution as, for example, by the application of heat, This procedure is preferably carried out in the presence of a protective colloid such as gum arabic or casein in order to prevent undue agglomeration of the liberated rosin particles and to maintainthe particles in fine dispersion.

As aforementioned, the flameproofing salts can be dis- .solved directly in an ammonium resinate solution, in

which case it is generally desirable to incorporate a stabilizing agent, such as a protective colloid, to maintain the particles of free rosin liberated by the acidic salts .cient to impart substantial water resistance to the water- -soluble salts. This water resistance is apparently accomplished by the formation of a film or coating of rosin .about the salt crystals or particles during the drying operation when the rosin becomes fluid or plastic. The thicker the protective coating of rosin, the greater the water resistance of the water-soluble salts. In general, I

have found that about 2.5% by Weight of rosin on the Weight of the flameproofing salts provides substantial water resistance to the salts. For optimum results, I prefer to employ somewhat more rosin as, for example, at least about 4 to 5% by weight of the salts. The proportion of rosin to salts can be increased as much as desired as, for example, up to or more although practical limitations will be imposed by considerations of cost and the physical characteristics of the finished paper.

The rosin incorporated in amount sufiicient to impart substantial water resistance to the flameproofing salts also imparts substantial water'resistance to the paper, the degree of which varies to someextent with the particular amount of rosin introduced. By inhibiting Water solution of the salts and thus reducing their tendency to promote water diffusion through the paper, the protective rosin may also restore the water-resistant properties conferred on the fibers by the preliminary sizing in the beater.

Any suitable water-soluble flameproofing salt or mixture of salts can be used for my purpose so long as the salt or mixture of salts is neutral or, preferably, acidic in character. An alkaline salt or mixture of salts, the efiective pH of which is alkaline, is objectionable apparently bacause of the tendency to saponify the rosin in the finished paper, thereby solubilizing the rosin and impairingits waterproofing properties. Suitable salts and their specific characteristics are well known in the art and include, for example, ammonium sulfate, monoammonium The flameproofing agents can be employed individually or in mixtures. An alkaline salt such as diammonium orthophosphate can be used very successfully so long as sufficient acid salt, such as ammonium sulfate or monoammonium orthophosphate is combined with it to impart a Generally speaking, because of their efiicacy, low cost and availability, I prefer to employ ammonium sulfate, monoammonium orthophosphate, mixtures of these salts'or mixtures of either or both with other flameproofing salts such as diammonium orthophosphate. It will be understood that the term flameproofing salts as employed in this specification and claims refers to an acid salt or mixture of acid salts or to mixtures of 'saltsfthe' eifctive 'pH of which is neutral to acidic although at least one of the components can be alkaline per se. The flameproofing rosin suspension itself can be alkaline. The presence of ammonia, for example, can, in some cases have the desirable effect of facilitating penetration of the paper by the treating fluid. However, such :alkalizing components should be of such character that the imparted alkalinity is dissipated in the finished paper as, for example, by volatilization during the drying.

The flameproofing salts, which are dissolved in the aqueous phase of the rosin suspension, are incorporated in the paper in an amount sufiicient to provide the desired fiameproofness. The actual amount incorporated into the treating suspension is, of course, determined by conditions such as the total fluid pickup by the paper under the particular conditions of application, which in turn determines the requisite solids concentration in the suspension. For example, where the fluid pick-up is 50% by weight of the paper, solids concentration in the suspension should be twice the desired solids add-on on a dry paper basis,

I have found that, in general, it is desirable to incorporate at least about 15% by weight of the flameproofing salt and preferably at least about 17% into the paper in order to impart flameproofing which meets optimum standards in terms of fire resistance, after flaming and afterglow. Should there be any material in the paper, such as an alkaline material, which would tend to decompose the fiameproofing salts, .enough more of the latter should be incorporated to make up the loss. In general, more .of the flameproofing salts is required than in the case where an unsized, absorbent paper is impregnated with the salts unprotected by the rosin. An add-on of about 10 or 11% salts is usually adequate to fiameproof an unsized paper. However, the increased amount of flameproofing salts required according to my process is more than compensated for both by the water-resistance of the salts and the highly desirable size properties of the paper. The increase in salt requirement is apparently due to the fact that a considerable proportion of the salts is external to the paper fibers and that additional salts are needed to protect the added rosin.

The paper can be impregnated with the rosin suspension containing the flameproofing salts in solution in any desired and convenient manner, as by dipping, spraying, rotating brushes, contact rolls and the like.

Example II Paper furnish comprising sulfate kraft fiber which had been sized in the beater with 0.1% rosin size and 0.5% alum was formed in the usual way on a Fourdrinier paper machine into paper having a basis weight of lbs. per ream of 500 sheets, size 24 by 36 inches. The paper, tested according to ASTM designation D 779-54, had a -water resistance of 38 seconds.

- The pick-up increased the dry weight of the paper from 40 to 48 lbs. perream.

The finished paper was tested forflammability and afterglow in accordance with ASTM designation D 777-46 with the following results:

Char length:

Maximum 3% inches. Average 3% inches. Minimum 3 inches.

After flame; Less than '1 second.

These results conform with T55282, Commercial Standard for Flame-resistant Paper and Paperboard, recommended by the U. S. Department of Commerce.

The finished paper was also tested for water resistance in accordance with ASTM designation D 779-54:

Seconds Maximum resistance 65 Average resistance 42 Minimum resistance 34 These results indicate excellent size properties.

The paper was found to retain its flameproof properties, substantially unimpaired, during the foregoing water-resistance test for a period of up to about 25 to 30 seconds.

(B) Paper made in similar fashion to the foregoing, including the beater sizing, except that the rosin was omitted from the flameproofing solution, while exhibiting similar flame resistance properties, gave a water resistance test of about 1 second and substantially lost its fiarneproofness within 1 second after the water contact.

Example 111 Paper processed in substantially the same way as that in Example II, A and B was suspended for 12 hours under conditions of 80% humidity and then tested for flameproofness. Paper A, namely the paper which had been treated with a rosin-flameproofing salt suspension retained its flameproofness substantially unimpaired. Paper B, which had been treated with a flameproofing salt without rosin, lost flame resistance to the point where it was far below acceptable standards.

Although this invention has been described with reference to illustrative embodiments thereof, it will be apparent to those skilled in the art that it may be embodied in other forms but within the scope of the appended claims.

I claim:

1. A process for flameproofing paper which comprises impregnating an at least partially sized paper sheet with a suspension comprising rosin dispersed in a solution of water-soluble flameproofing salts, the flameproofing salts being characterized by a maximum pH of about 7 and being incorporated in the paper in an amount sufficient to render said paper substantially flameproof, said rosin being incorporated in the paper in an amount sufficient to impart substantial water resistance to said watersoluble flameproofing salts.

2. The process of claim 1 in which the flameproofing salts are characterized by an effective pH of less than 7.

3. The process of claim 1 in which the paper prior to impregnation With the flameproofing salts is sized to at least about 7 seconds water resistance as tested according to ASTM designation D 779-54, the flameproofing salts are incorporated in the paper in an amount comprising at least about 15% by weight of the paper and the rosin comprises at least about 2.5% by weight of the flameproofing salts.

4. The process of claim 3 in which the flameproofing salt comprises at least about 17% by weight of the paper and the rosin comprises at least about 5% by weight of the flameproofing salt.

5. The process of claim 1 in which the flameproofing salts comprise ammonium sulfate.

6. The process of claim 3 in which the flameproofing salts comprise ammonium sulfate.

7. The process of claim 4 in which the flameproofing salts comprise ammonium sulfate.

8. The process of claim 1 in which the flameproofing salts comprise monoammonium orthophosphate.

9. The process of claim 3 in which the flameproofing salts comprise monoammonium orthophosphate.

10. The process of claim 4 in which the flameproofing salts comprise monoammonium orthophosphate.

11. The process of claim 1 in which the flameproofing salts comprise ammonium sulfate and an ammonium salt of phosphoric acid.

12. The process of claim 3 in which the flameproofing salts comprise ammonium sulfate and an ammonium salt of phosphoric acid.

13. The process of claim 4 in which the flameproofing salts comprise ammonium sulfate and an ammonium salt of phosphoric acid.

References Cited in the file of this patent UNITED STATES PATENTS 170,829 Dunham Dec. 7, 1874 1,248,092 DRohan Nov. 27, 1917 1,310,841 Robinson July 22, 1919 1,581,779 Brandt Apr. 20, 1926 2,128,296 Baker Aug. 30, 1938 2,178,625 Clayton Nov. 7, 1939 2,357,725 Bennett Sept. 5, 1944 2,387,865 Van Kleeck Oct. 30, 1945 2,553,154 Voigtman May 15, 1951 2,566,964 Scholz Sept. 4, 1951 2,611,694 Becher Sept. 23, 1952 2,640,000 Seyb May 26, 1953 2,711,370 Lurie June 21, 1955 

1. A PROCESS FOR FLAMEPROOFING PAPER WHICH COMPRISES IMPREGNATING AN AT LEAST PARTIALLY SIZED PAPER SHEET WITH A SUSPENSION COMPRISING ROSIN DISPERSED IN A SOLUTION OF WATER-SOLUBLE FLAMEPROOFING SALTS, THE FLAMEPROOFING SALTS BEING CHARACTERIZED BY A MAXIMUM PH OF ABOUT 7 AND BEING INCORPORATED IN THE PAPER IN AN AMOUNT SUFFICIENT TO RENDER SAID PAPER SUBSTANTIALLY FLAMEPROOF, SAID ROSIN BEING INCORPORATED IN THE PAPER IN AN AMOUNT SUFFICIENT TO IMPART SUBSTANTIAL WATER RESISTANCE TO SAID WATERSOLUBLE FLAMEPROOFING SALTS. 